The present invention is directed generally to memory access, and in particular to power dependent memory access.
Contactless integrated circuit (IC) cards, also known as chip cards or smart cards, operate on the basis of communication by a radio frequency (RF) or electromagnetic field with a read and/or write interrogating device, generically referred to as a reader.
In contactless IC card applications, the reader typically transmits an RF carrier wave having a carrier frequency of 13.56 MHz. This transmitted carrier wave serves on the one hand to set up a communication between the card and the reader according to an established communication protocol, and on the other hand to power the contactless card, which derives the energy required for its operation by induction.
A minimum transmission field strength is required to power a contactless IC card for operation. This minimum transmission field strength is significantly impacted by properties of the contactless IC card's internal memory. These properties include average current during a read/write access and peak currents during a read/write access. While these properties are aspects of most memories, they are most critical in non-volatile memories (NVMs) due to the high currents required to generate programming voltages.
In order to reduce the contactless IC card's power consumption and thus the minimum transmission field strength required to power the card, the current expended during a read/write access of the card's memory should be reduced. One way to reduce this current is to reduce the speed of memory access. However, reduction in access speed has the undesired result of a longer programming time.
Another way to reduce this current is to reduce the number of bits accessed in parallel. In other words, rather than program all bits at once, the programming is divided into sequential steps. However, the number of bits to be accessed is static and must be determined during the memory design stage.